add missing class to make the buildDashboard example working
fix software development plugins documentation
Convert the BuildDashboardPlugin to Java and clean it up a little.
Add the ReportingExtension to the DSL ref.
Fix an unchecked assignment.
Some work on the build dashboard user guide chapter.
Drop section describing the requirements of multi project maven builds for conversion.

What was there was very difficult to understand, and more or less amount to a common sense assumption of the requirements.
Fix compile error by suppressing warning.
Some tidy-ups of converting from Ivy to Gradle identifiers.
Moved a class that is only used by tests into the test source directory.
Tweak to warning message.
Some generics
Added missing space to a few places in user guide.
Fixed typo.
Some minor edits to javadocs
Some minor cleanup of the DistributionPlugin internals.
Build with a recent nightly.
Work on the distribution plugins docs.
Be explicit about requiring an isolated gradle user home dir for this test.
Fix the content hierarchy in this user guide chapter.